1. Field of the Invention
The present invention relates to cation exchange fibers having a high capacity of ion exchange and a low degree of swellability as well as physical properties which allow them to withstand processing such as in a carding operation.
2. Description of the Prior Art
Ion exchange resins have been used since old times in a variety of fields including treatment for civil water, waste water, toxic gases, and others.
As regards the shape of the resin, fibers are preferable to grains since the former has a larger surface area than the latter and therefore can increase the ion exchange speed. Moreover, fiber shape is more advantageous in industrial use since fibers are freer in use shape. Up to this time therefore many attempts have been made on ion exchange fibers.
For example, in KOGYO KAGAKU ZASSHI, 68 (7) 1304 (1965), it is described that excellent cation exchange fibers can be obtained by introducing carboxyl groups into acrylonitrile (hereinafter referred to as AN) polymer fibers by hydrolyzing nitrile groups of the AN polymer fibers.
By this method, however, with an increase in the ion exchange capacity, fiber physical properties such as tensile strength, etc. will fall, and for example, when carboxyl groups of more than 3 m eq/g are introduced, such fibers, though they hold fiber shape, can not retain physical properties which allow them to withstand processing such as in a carding operation.
In Japanese Patent Publication No. 38596/1979, a method of producing cation exchange fibers is proposed wherein AN polymer fibers are reacted with hydrazine to give a prescribed anion exchange capacity, followed by hydrolysis of remaining nitrile groups.
By this method, however, with an increase in the ion exchange capacity, the fiber physical properties also fall greatly and moreover since the degree of swellability increases extremely, there will occur problems of clogging and deterioration upon use. Consequently, even though the ion exchange capacity may be heightened, the rate of its utilization has to be low, and finally, such ion exchange fibers fail in displaying a high ion exchange ability.
The object of the present invention is therefore to provide cation exchange fibers which have no such problems as mentioned above that have become apparent from various experiments, and which are given a high ion exchange capacity and a high utilization rate of ion exchange radicals while retaining fiber physical properties without problems in practical use, with the degree of water-swellability of which being controlled to below a definite level, thereby to fully display advantages of the high ion exchange speed, free shape, etc. coming from the fiber's own intrinsic nature.